The present invention relates to interstitial brachytherapy sources for use in the treatment of tumors, cancers and other proliferative tissue.
Brachytherapy is the science of applying radioactivity to living tissue over relatively short distances in order to retard cell growth or induce cell death in a targeted area. When cancerous and other proliferative tissues are to be treated, it is desirable to target the radiation therapy with a high degree of specificity to avoid damaging irradiation of surrounding healthy tissue.
External radiotherapy systems administer radiation in a directed beam. Even when the tissue to be treated falls within a therapeutically active depth for a given beam energy, the intervening and surrounding healthy tissue is irradiated needlessly.
Interstitial brachytherapy sources allow radiation to be targeted more specifically and more deeply in living tissue. The use of radioactive seeds in the treatment of prostate tumors is one example of an interstitial brachytherapy source. Such seeds are usually loaded into a delivery vehicle which is then removed from the tissue after the seeds are implanted.
One disadvantage of brachytherapy seeds is that they are discrete, or xe2x80x9cpointxe2x80x9d, sources of radiation and thus do not provide a continuous or uniform dosage over any length of treatment area. To provide a semblance of dosage continuity, seeds would need to be closely and uniformly spaced, and this is difficult and time consuming, without reliable assurances that the seeds will remain as placed. Because the seeds can migrate in the tissue, they may become either too closely spaced or too far apart, which further detracts from optimal dosage delivery. Thus, they cannot reliably assure a constant or uniform dosage to the targeted tissue, and they may cause unnecessary radiation damage to surrounding healthy tissue.
Further complicating the application of interstitial brachytherapy is the fact that while a particular radiation distribution may be preferred based on the treated volume prior to implantation of the source, the tissue constituting the volume to be treated changes shape and size (as, for example, enlarging and swelling caused by localized edema due to the trauma of the insertion of the source, and shrinking due to subsequent radiation treatment of the tissue). Such changes in the shape and size of the tissue can change the preferred radiation distribution. However, current brachytherapy sources are not believed to adequately address this problem.
For example, many tumors, tumor beds and lesions are effectively treated with radiation administered from an interstitial brachytherapy source in the form of radioactive wires, rods or ribbons. However, these sources are in fact packages of seeds which are held together inside a catheter, sheath, tube or the like. Further, even in such xe2x80x9cextendedxe2x80x9d sources, the activity is present at discrete locations along the length of the source instead of continuously along the length of the source. This produces an inferior dose distribution and may create an unacceptably high contact dose in the active regions in which the source is located. One consequence of this is the possibility that such treatment could produce cosmetic damage, such as dimpling or holes, in tissues such as that of the breast. In addition, these extended sources are not continuously flexible. Rather, they are flexible only between the seeds and rigid in the areas at which the seeds are located. Rods are clearly not flexible, and even the wires and ribbons are made from heavy-gauge stock which is not flexible. Finally, none of these extended sources is extendible in the axial direction, nor are they designed for axial expansion. Rods and wires would break if axially expanded, and ribbons, if bent or stretched, would lose their characteristic source-to-source spacing. Thus, all of the prior art sources are inadequate in adapting to the changing size and shape of the treated tissue.
Stents have also recently been promoted for brachytherapy treatments. Radioactive stents act as devices which radially expand into place when inserted into a lumen at a treatment site and deliver radiation to maintain the patency of the lumen and prevent restenosis. A stent, once deployed, is typically relatively stiff in the radial direction so as to support the surrounding tissue to prevent restenosis, and also relatively stiff in the axial direction so as to resist being dislodged from its initial position.
The goal of stent brachytherapy is to inhibit or retard localized regrowth of cells and the acquisition or deposition of extracellular media on the inner surface of the vessel. A typical radioactive intensity for a radioactive stent is in the neighborhood of about 1 to 20 microCuries, so as to deliver a nominal radiation dosage to a surrounding vessel of about 15 Gy at a distance of about 1 mm from the surface of the stent. A total volume of tissue to be treated with a radioactive stent is typically about 0.4 mm3.
The effective treatment of tumorous tissue, on the other hand, requires that all cells in the affected region be ultimately eradicated. It is reported that if even 30 cancerous cells per cubic millimeter survive a cancer therapy, the cancer can regrow at that location. As an example, brachytherapy seeds typically have an activity of about 1.4 milliCuries per seed, and nominally one hundred seeds are used to treat, for example, a prostate cancer, for a total activity of about 140 milliCuries. The typical prescribed dose is in the range of 80 to 200 Gy, and for palladium-103, commonly used in prostate tumor therapy, it is about 115 Gy. Seeds are typically spaced 1 cm apart, although uniform seed spacing and uniform dosages cannot be assured. A total volume of tissue to be treated with seeds is typically about 60 cm3.
The dosages and activities required for effective tumor treatment are much higher than for stenosis prevention. Such dosages and activities are not typically provided with radioactive stents.
Therefore, the effectiveness of prior art interstitial brachytherapy sources and devices such as stents is limited in tumorous and other proliferative tissue which may undergo changes in size and shape during therapy.
It is therefore an object of the invention to provide an interstitial brachytherapy source which can shrink and grow in response to changes in the size and shape of tissue with which the source is in contact. In particular, it is an object of the invention to provide a flexible, continuous, axially elastic interstitial brachytherapy source.
The invention comprises, in one aspect, an interstitial radioactive implant, or source, which is capable of changing its shape and/or size in substantially all directions in response to changes in the shape and/or size of tissue with which the implant is in contact. In a preferred embodiment, the radioactive implant defines a substantially continuous source of radiation that extends along a principal axis. If the tissue behavior warrants, the source is capable of expanding and contracting in the direction of the principal axis, as well as flexing in directions other than the principal axis.
In one embodiment, the radioactive source comprises a wire in the form of a coil. The diameter of the wire is preferably between about 10 and about 250 micrometers. The outer diameter of the coil is preferably between about 25 and about 1500 micrometers.
In a preferred embodiment, the radioactive wire coil has a specific activity of at least 10 microCuries/cm. A preferred range of specific activity is between about 100 microCuries/cm and about 50 milliCuries/cm.
The coil may be manufactured to virtually any length and then cut to a length which is appropriate for treatment of the lesion, tumor or cancer of interest.
The source may include tissue anchors at opposite ends thereof and/or at intermediate points to fix the source in the tissue to be treated.
These and other objects and advantages of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the apparatus possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure, the scope of which will be indicated in the claims.